Gear-adjusted potentiometer



Aug. 4, 1-970 R. D; MlCHlK ET AL GEAR-ADJUSTED POTENTIOMETER Filed Jan. 10, 1969 INVENTORS ROBERT D. M/CH/K, W/LBUR 7' HARD/SON 6:

ROBERT M 5PORRONG United States Patent O 3,522,572 GEAR-ADJUSTED POTENTIOMETER Robert D. Michik, Wilbur T. Hardison, and Robert N.-

Sporrong, Riverside, Califi, assiguors to Bourns, Inc., a corporation of California Filed Jan. 10, 1969, Ser. No. 790,335 Int. Cl. H01c 9/02 US. Cl. 338-171 4 Claims ABSTRACT OF THE DISCLOSURE CROSS-REFERENCE In certain respects the potentiometer and invention disclosed herein are related to like items disclosed in application of Robert D. Michik, Ser. No. 790,344, filed on even date herewith.

BACKGROUND OF THE INVENTION Gear-adjusted potentiometers, commonly called square potentiometers, have heretofore been of constructions such as to require a considerable amount of painstaking manual assembly operations. For example, following insertion of driving screw means and the driven-gear means, careful insertion of retainer means for each of those elements was required. In addition, careful hand-welding of terminal pins or leads to the ends of the resistance element and the collector was necessary. The present invention provides a construction in which necessity for such delicate manual operations is avoided, and such that semiautomatic mechanical assembly of the potentiometers is permitted.

SUMMARY OF THE INVENTION According to the present invention, terminal members are molded in place in an insulative box-like body or principal housing member of a potentiometer with one of the terminal members protruding upwardly from adjacent the center of the floor of the box and two of the others thereof extending into respective regions in which resistance-element terminations will be disposed when the cover of the housing is put in place. The upwardly-protruding pin defines an axis and serves as a gudgeon for a contact-carrier disc and also serves as a means for retaining the disc in place and as a conductive return for the contact device which brushes on the resistance element. The other two molded-in terminal members are disposed and arranged for automatic connection to respective resistance-element terminations by a dip-soldering procedure and machine. The body of the housing has an upstanding hub or boss around the centrally disposed pin, which boss serves as a gudgeon upon which the contact-actuating gear is rotatably supported. The contactactuating gear, by action similar to a friction clutch, drives a centrally apertured disc-like contact carrier or device, the contacts of which brush on a resistance element. A driving gear, which in the exemplary potentiometer is a wormscrew, is disposed with a head end accessible at the exterior of the housing and with the thread in driving engagement with the driven gear. The driven gear has a raised rim and a depressed central area, whereby the rim is at an elevation above the end of the gudgeon or boss.

Following installation of the driving gear or wormscrew in a manner and by means taught in the aforementioned application, Ser. No. 790,344, and dropping or placement of the driven gear on the gudgeon or boss, the centrally apertured metal disc-like contact carrier is mounted on the pin above the boss and gear. Then, while the central portion of the resilient contact carrier disc is pressed down into a slightly concave shape by pressure applied thereon adjacent to the upright pin terminal member, the pin is deformed, as by flattening with a pinching or shearing device, closely adjacent the upper surface of the disc. Thus in one very simple operation the disc or contact carrier is sprung or stressed downwardly thus retaining the driven gear in place in mesh with the driving screw, and concurrently assuring effective electrical connection between the contact carrier and the pin, all without the usual retainer clip or like additional means being applied or required. Following the preceding operations, a cover or lid, bearing thereon a resistance element and termination films from the respective ends of the element to edges of the cover, is applied so as to bring the films substantially into contact with respective ones of the terminal members embedded in the box or body of the housing; or into contact with conductive films leading to the latter terminal members. Optionally, thereafter a wave soldering or conductive cementing operation may be performed to improve effective electrical unity of the respective conductive members, and the lid is sealed or potted to the box to complete the potentiometer. Thus, by particular placement of termination conductors, embedding of terminals, and utilization of deformation of a terminal member to form from the same member a retaining member, a contact-carrier tensioning member for stressing a clutch device, and a direct-connection return bus for the potentiometer, manufacture is considerably simplified and made less expensive. Further, by choice of shape and arrangement of gear and clutch members, the tensioning of the contact-carrier disc serves to permit over-driving of the gearing without movement of the con tacts oif the resistance element or damage to the parts, and serves to retain the driven and driving gears in place. A plurality of advantages are gained by molding the body of the housing with terminals as inserts embedded in the insulative plastic compound during molding, namely, the terminals are proofed against being pulled out, all problems of sealing the terminals against ingress of moisture or undesired materials are obviated, and fewer and simpler parts are required.

DESCRIPTION OF THE DRAWINGS A preferred exemplary arrangement and embodiment of components according to the invention is illustrated to a grossly exaggerated or enlarged scale chosen to facilitate clear illustration of details. In the drawings:

FIG. 1 is a pictorial view of an exemplary potentiometer, to grossly enlarged but arbitrary scale;

FIG. 2 is a plan view of the potentiometer depicted in FIG. 1, to a different and larger scale, with a cover and resistance element and appurtenances removed to show details;

FIG. 3 is a sectional view of the exemplary potentiometer, the section being as indicated by indicators 3-3 of FIG. 1;

FIG. 4 is a face view of the molded body or box of the exemplary potentiometer shown in section in FIG. 3, with terminal members molded in, and prior to deformation of a centrally located pin portion of one terminal;

FIG. 5 is a face view of a dual-purpose driven gear and clutch member of the exemplary potentiometer;

FIG. 6 is a diametrical sectional view of the gear shown in FIG. 5;

FIG. 7 is a plan View of a driving gear or wormscrew of the exemplary potentiometer;

FIG. 8 is a plan view of a multiple-function resilientmetal device comprised in the potentiometer of FIGS. 1, 2 and 3;

FIG. 9 is a sectional view of the device shown in FIG. 8, the section being taken transversely and through the axis of the device; and

FIG. 10 is an inside face view of a cover comprising a second principal housing member of the potentiometer of FIGS. 1, 2 and 3, and appurtenant resistive and conductive components carried by the cover.

DESCRIPTION OF THE ILLUSTRATED POTENTIOMETER In FIG. 1, the exemplary potentiometer is denoted generally by number 12 and as comprising a box-like body 14 from which protrude first, second and third pin-terminal members S, T and U and a head 30h of a driving-gear; the potentiometer also comprising a lid or cover 20. As is indicated in FIGS. 2, 3 and 4, the three terminal members are incorporated into the box-like body 14 by insert-molding procedures, whereby a portion of each terminal member is exposed at the interior of the body for direct electrical connection to an appropriate respective component in the chamber formed by the body and cover.

As is indicated in FIGS. 3 and 4, the body 14 is formed, as by injection molding of insulative synthetic polymer, with first, second, third and fourth wall portions 14d, 14b, 14c and 14a, respectively, a floor or bottom 14:: and an upstanding central boss 14 in which is embedded an upstanding inner end portion Tu of terminal member T. Wall 14b is bored or formed with a bore 14g for reception of driving gear means in the form of a wormscrew 30 (FIG. 2). The bore is extended as a partial bore or seat 14s along wall 14a. From floor He and wall 14a there extends inwardly into the box an integral camfaced abutment 14k of angular or L-shaped configuration, the inclined surface of which next-adjacent seat 14s provides a cam face 14k. The box or body 14 of the potentiometer provides a generally annular lower cavity encircling boss 14; and a generally circular upper cavity above the boss. The abutment 14k protrudes into the annular cavity, which communicates with bore 14g. The walls and floor of body 14 form a chamber, and are shaped to cooperate with and accommodate the rotary components presently to be described.

Disposed for rotation on the upstanding boss 14] in the lower cavity of the box is a dual-purpose member here called for brevity a driven gear 16 (FIGS. 3, 5 and 6). The lower portion of the gear is formed with a hub and teeth such as 161, and with a bore 16b for rotational bearing on the boss 14 The upper portion of the gear is extended radially outwardly to form a flange which is provided on its upper annular face with a series of serrations or like friction-augmenting formations which in the illustrated exemplary structure are radial ridges 161 as shown in FIG. 5. The formations may, of course, be radial grooves or depressions. The serrated flange serves as one elemenl of a friction clutch.

With particular reference to FIGS. 2 and 3, there is disposed for rotation on the upwardly protruding end portion Tu of terminal member T, a disc-like contact device or carrier, 18, details of which are shown in FIGS. 8 and 9. The contact device 18 has an aperture 18a for close bearing fit on and adjacent the upper end of portion Tu of terminal T, and has a series of protuberances 18p formed along a part of the periphery on the lower face thereof. The protuberances are formed by depressing portions of the plate or disclike body of the device by die means, and are dimensioned and spatially arranged to fit between, and cooperate with, the formations 161- on gear 16. The contact device 18, which is made of resilient metal, carries contact means which in this example comprises a set of resilient contact fingers 18 (FIG. 8) formed integral with the body of the disc by punch-forming operations. The outer end of each finger is formed into a contact disposed and adapted to brush on a resistance element presently to be described.

After the driving gear or screw 30 is pressed into place in bore 14g and its inner head 30i engaged with the interior face of abutment 14k in a manner more fully explained in the noted companion application, Ser. No. 790,344 of Robert D. Michik, and driven gear 16 is mounted on boss 14 and the contact device or carrier 18 on the upstanding end Tu of terminal T, the central area of the carrier, around portion Tu of the terminal T, is forced downwardly into the shallow depression formed in the upper face of driven gear 16, and the immediately adjacent exposed end portion of Tu is deformed as by shearing and flattening. As is indicated in slightly exaggerated form in FIG. 3, the upper face of the contact carrier is thus sprung to concave shape, with the deformed end of Tu restraining the carrier from returning to flat configuration. Thus, the stressed contact-carrier presses down on the annular rim of driven gear 16, thereby holding that gear on boss 14 and causing the gear 16 to restrain screw 30 from moving laterally from seat 14s and inner head 30: from moving out of engagement with abutment 14k. Thus, by the noted arrangement and configuration of parts, the screw is held against exit from the housing by gear 16, gear 16 is held firmly in engagement with the driving gear or screw by contact device 18, the clutch mechanism formed by the coacting interrupted annular faces of the contact device and the driven gear are held firmly in resilient frictional engagement by the concave stressing of the contact device, and the contact device is maintained under the requisite stress and in excellent and effective electrical communication with terminal T. No snap-ring or similar part is required to retain the gear and contact device in operative and cooperative relation, as is usual in gear-actuated otentiometers. Nor is any electrical connector intermediate the terminal T and the contact carrier required, nor is a spring-washer or like device required to assure good electrical continuity in the contact-to-terminal electrical path in the potentiometer.

The contact carrier 18 is driven, incident to external rotation of driving gear or screw 30, by clutching action between the interengaging faces of the gear 16 and carrier; and such rotational movement carries the contacts of the fingers 18 along an arcuate brushing path until further rotation is stopped by collision of a radial extension or stop 18s (FIG. 8) on the contact carrier with a fixed abutment or stop 14s (FIGS. 2 and 4) formed on the interior of wall 14d of the housing body. After such collision, further driving of gear 16 by continued rotation of screw 30 merely causes slipping of gear 16 relative to the contact carrier, the ridges 16r on the gear riding past and deflecting the protuberances 18p of the contact carrier.

The fingers 18] (FIGS. 8 and 9) are formed most conveniently by a punching operation in which a portion of the disc of the metal contact carrier is removed and a plurality of fingers bent up and formed to shape as indicated. When the contact carrier is mounted on the inner end of terminal T by passinng the upper end of portion Tu of the terminal through the close-fitting aperture 18a of the carrier, the fingers of the contact device extend upwardly away from the disc of the carrier, into a position for engagement with a resistance element which is mounted on, or formed on, the inside of the cover or lid of the potentiometer.

The cover of the illustrated potentiometer is aceramic wafer 20 (FIG. of steatite, alumina, or the like insulation, and is shaped to closely fit into the complementary open upper portion of the housing box 14 and to rest there on ledges such as those indicated at 14x at the corners of the box, in FIG. 4. 0n the inner face of the ceramic substrate or wafer 20 is an arcuate resistance element 20a (FIG. 10) which preferably is a cermet element but may if desired be of metal-film or carbon or other resistance material. At either end of the element there is applied a conductive film, such as 200 which electrically connects with the respective electrical end of the element and extends over a respective notched corner of the wafer as indicated. Thus when the cover is pressed into place to cover the chamber containing the operating parts of the potentiometer, the element 2202 comes into contact with fingers 18 and depresses and resiliently stresses the latter; and each of conductive films 200 is brought nearly into contact with a respective one of terminals S and U. To aid in assuring low-resistance electrical connection at the junctures of the conductive films with the terminals, small amounts of conductive cement or the like may be applied over the mating surfaces thereof prior to placement of the cover on the body 14.

Following placement of the cover on the body 14, the cover may be sealed in place with a sealant R (FIG. 3) applied around the exterior periphery of the cover and adjacent walls'of the body 14. Thus the potentiometer is sealed against ingress of undesired substance by the sealant and by an O-ring seal 32 mounted on the shank of wormscrew 30 and disposed in bore 14g.

To attain more secure anchorage of the terminals S, T and U, and more effective sealing of the potentiometer, the terminals are preferably upset as indicated, and terminals S and U are swaged to form an effective head or large exposed surface at the interior of body 14, as indicated in FIGS. 2 and 4. The swaged ends aid in effecting excellent electrical connection of the terminals to the conductive films 200.

Details of the driving gear or wormscrew, such as the inner head 30i, beveled end 3%, shoulder 30k, thread 30t, groove 30g, shank 30s and slotted head 30h, together with cooperating details of the housing and of gear 16 whose teeth 161? engage the thread 30t, are set forth in the noted companion application, to which reference may be bad if necessary for details not per se necessary to the presently-claimed invention.

We claim:

1. A gear-adjusted potentiometer comprising:

first means, including housing means comprising a molded insulation body and a cover and providing an interior chamber;

second means, including first, second and third terminals, said second terminal having an intermediate portion embedded in said body and having an inner end protruding into said chamber along a first axis defined thereby to provide a conductive gudgeon and having an enlargement forming a deformity at the end of said gudgeon;

third means including a resistance element mounted on said first means and having a surface exposed in said chamber, and means connecting end portions of said element to said first and third terminals; fourth means, including interengaging driving and driven gear means confined to rotation about respective axes by said first means, the axis of said driven gear means being coincident with said first axis and said driven gear means having a friction face exposed in said chamber;

fifth means, including a resilient disc-like conductive contact device mounted on said second terminal for rotation about said first axis with an outer face portion thereof in frictional contact with said friction face of said driven gear means, the central portion of said contact device being resiliently stressed downwardly and retained under stress by said deformity at the said end of said gudgeon, and said contact device having resilient contact finger means extending toward said cover and resiliently brushing said resistance element;

whereby said second terminal is directly connected electrically to said contact device at said deformity and said deformity stresses said contact into resilient frictional engagement with said driven gear means for rotation of said contact device by said driven gear means.

2. A potentiometer as defined in claim 1, in which said molded insulation body is of open-top box form having side walls and a bottom, said first, second and third terminals being pins protruding from the outer face of a first of said side walls and said second terminal being embedded in said bottom and extending into said chamber normal to said bottom; and said driving gear means having an end exposed at a second side wall of said body opposite said first side wall, whereby said potentiometer terminals may be inserted into a circuit board or like support and access to the potentiometer for adjustment provided by said exposed end of said driving gear means.

3. A potentiometer as defined in claim 1, in which said body comprises an open-top box-like member having a bottom and a boss upstanding therefrom coaxial with said first axis and a portion of said second terminal extending along said axis in said boss and protruding therefrom into said chamber, said driven gear having a generally depressed annular central hub journaled on said boss and a raised flange portion presenting said friction face, said contact device being stressed into slightly concave configuration by said deformity to stress said outer face portion thereof into firm engagement with said friction face of said driven gear means,

whereby effective low resistance connection between said second terminal and said contact device is maintained without other parts.

4. A potentiometer as defined in claim 3, in which said driving gear means is a wormscrew gear disposed along a bore and seat formed in said body, and wherein said flange portion of said driven gear means overlies a portion of said wormscrew gear and retains the latter in said seat,

whereby said deformity of said second terminal serves to tension said contact device against said flange portion and thereby to retain said driven and driving gear means in place on their respective axes.

References Cited UNITED STATES PATENTS 3,096,498 7/1963 Tumbusch 338-162 3,201,737 8/1965 Mathison.

LARAMIE E. ASKIN, Primary Examiner D. A. TONE, Assistant Examiner US. Cl. X.R. 338-162 

